This invention relates generally to cartridge-type electrical fuses, and more particularly to a mating device which facilitates insertion of such fuses into a fuse holder and the removal thereof, the fuse mate also carrying out other useful functions.
A fuse is a protective device containing a short length of special wire that melts when the current therethrough exceeds the rated value for a given period. Because the fuse is inserted in series with the circuit to be protected, it opens this circuit automatically in the event of an unacceptable overload.
The fuse commonly used in conjunction with electronic equipment is of the so-called cartridge type. This is constituted by a tubular casing of glass or other clear insulating material whose ends are enclosed by metal terminal caps, the fuse wire extending through the casing and bridging the caps. Since the fuse wire is visible through the transparent casing, should an overload occur which melts the wire, the blown condition of the fuse then becomes evident. In some cases, the casing is of opaque or ceramic material.
Cartridge fuses are socketed in holders formed by an insulating base on which a pair of metal spring clips is mounted to engage the terminal caps of the fuse, the circuit connections being made to the clips. In many instances, an array of parallel holders are formed on a common base so that the fuses are then very close to each other. Normally, to install a fuse, one grips the casing thereof between the thumb and forefinger and then pushes the fuse into the holder clips. And to remove a fuse from the holder, one again grips the casing with the fingers to pull the fuse from the holder clips.
To insure efficient electrical contact between the holder clips and the fuse terminal caps, the clips are designed to apply a substantial clamping pressure on the caps. These pressures make insertion and removal of the fuse quite difficult, which difficulty is compounded when the fuses are small or where a family of fuses are very close to each other. Moreover, because at least one holder clip is alive, and the gripping fingers are quite close to the terminal caps, there is a danger of shock, particularly if resistance is experienced in removing or inserting a fuse in the course of which the fingers are shifted toward the caps.
Because of problems encountered in removing cartridge type fuses, the use of screw drivers to pry the fuse from the holder is not uncommon. This can lead not only to fracture of the relatively delicate fuse casing, but it may also result in the short-circuiting of adjacent fuse holders.
To overcome these difficulties, various forms of cartridge-type fuse extractors have heretofore been proposed, all of which include some means to grip the fuse casing and a handle to pull the clamped fuse out of the holder. Thus U.S. Pat. No. 1,380,242 shows a fuse extractor having a pair of jaws adapted to receive and retain a cartridge fuse, with a long handle to isolate the user from the fuse terminals. The extractor is designed so that after a fuse is inserted in its holder, the jaws can be disengaged therefrom. Other forms of fuse extractors or pullers adapted to engage, and then release the fuse, are disclosed in U.S. Pat. Nos. 2,454,870; 3,215,006; and 3,654,824.
In fuse extractors or pullers of the type heretofore known, the tool is only put to use when a fuse is in need of insertion or removal, so that under normal circumstances, the cartridge fuses in a given piece of electronic equipment are socketed in their holders with their live terminals exposed. These fuses are disregarded unless an overload occurs which renders the equipment inoperative. It is only when this happens that one has occasion to check the several protective fuses to see which one is blown and in need of replacement.
Because all of the live terminals are exposed, in seeking to extract a given fuse, one may accidentally make contact with an adjacent live terminal. And since the fuse wire usually has a silver-like appearance and is enclosed within a clear casing, it is difficult to discern the condition of the wire in each fuse, especially when the fuses are in a closely packed array. Hence it may be necessary to extract the fuses one at a time with a suitable extractor and to examine each fuse in a good light, if one is available, to see whether it is blown. Finally, when the blown fuse is located, one must then replace this fuse with a fresh fuse having the same rating. This sometimes presents a problem, especially with small cartridge fuses whose ratings are inscribed on caps and are hard to make out.